This invention relates to an automatically operated fire extinguishing system usable for both electrical and gas residential cookstoves or ranges. More particularly, the invention concerns such a system which is mounted in a hood positioned over a residential stove or range.
Until relatively recently, automatic fire extinguishing systems for use with residential cookstoves and ranges have generally been concerned with extinguishing fires caused by fat burning in a commercial grease pot or kettle. Generally, the systems were solely concerned with extinguishing the fire. No provision was made for turning off electrical and gas burners of the stove. Consequently, the fire extinguishing system would extinguish the lighted burners of a gas stove while allowing the gas to continue flowing. This created the very hazardous condition of allowing unburned gas to flow from the burners, resulting in a situation in which a residence could fill with gas to dangerous levels and then explode. Or perhaps, on the other hand, the residents were exposed to the hazard of being asphyxiated by gas fumes. If the system is used with an electric stove, the burners could reignite spilled grease and fat once the fire extinguishing foam had dissipated. Moreover, these arrangements had no provision for sounding an alarm or deenergizing associated exhaust equipment.
U.S. Pat. No. 3,653,443 recognized the aforementioned difficulties with the prior art and provided a system for shutting off the stove, operating an alarm and deenergize exhaust fans. To the knowledge of the instant inventor, the concepts set forth in U.S. Pat. No. 3,653,443 have never been commercialized. The particular arrangement set forth in this patent has apparently not been commercialized because of the expense and difficulty in combining the concept of this patent with existing residential hood configurations. In other words, the particular structure disclosed in this patent is not readily retrofittable on existing residential stoves and stove hoods.
The prior art discloses numerous arrangements for automatically extinguishing stove fires. U.S. Pat. No. 4,256,181 discloses a fire extinguisher in combination with a hood. However, this patent requires a tube for conducting heat from the stove to a mechanism for operating the fire extinguisher. The operating mechanism includes a flammable fuel which generates heat in a hood above the stove making the operating system itself a fire hazard. The foam from the extinguisher is dispensed on the stove.
Other patents, such as U.S. Pat. Nos. 4,580,638; 3,584,688; 3,448,808; and 3,824,374, each disclose arrangements of cables and fusible links. However, these arrangements are not configured in a fashion which is readily adaptable to retrofitting in existing residential stove hoods or existing residential stove configurations. These arrangements are suitable for commercial kitchens rather than residential kitchens.
In order for an automatic fire extinguishing system to be widely used in residential kitchens, it is necessary for the system to be configured so that any home owner or resident with minimal mechanical skills can install the system. Ordinarily, household fire warning equipment designed to be installed by other than a qualified electrician cannot be powered from a source having a voltage in excess of 30 volts. Accordingly, in order to avoid the need for a qualified electrician, stove fire extinguishing systems must operate on less than 30 volts. None of the systems currently available meet this requirement, since they all require house line current.
If a range utilizes gas as a fuel and electric power to the house is interrupted, the systems currently available will not function properly during a power outage, since there is no power available to control the flow of gas to the gas burners. Accordingly, a very dangerous situation arises if there is a power outage during which a stove fire is extinguished, but gas continues to flow through the burners. The gas in and of itself can asphyxiate people in the house or can accumulate and explode when the electricity comes back on and generates a miscellaneous spark at a location in the house where gas has accumulated. The systems of the prior art do not protect residences in this particular situation.
This is not a problem unique to residential systems. As is set forth in the background discussion of U.S. Pat. No. 5,048,791, which the instant applicant's invention precedes, industrial systems have similar problems. According to U.S. Pat. No. 5,048,791, with industrial processes that involve hazardous or combustible substances, there is always a risk that a malfunction may result in damage of injury. To minimize the damage caused by such a malfunction, it is desirable to shut off the flow of hazardous substances as soon as the emergency is detected. This is particularly true in industrial operations that employ combustible fuels such as natural gas for heating in a furnace or oven. It is desirable to shut off the flow of combustible gas as soon as the fire condition is sensed.
Industrial furnaces and ovens are often equipped with automatic fire detection and extinguishing systems. Such systems are designed to sense a fire or an overheated condition and to spray CO.sub.2, dry chemical, foam or another type of fire extinguishing agent on the fire. When the fire extinguishing system is triggered, it is almost always desirable to shut off the flow of fuel to the furnace or oven. Of course, when the emergency condition is corrected, it is necessary to reinstitute the flow of gas to that the process may be restarted.
Various types of systems have been devised which use conventional valves to shut off the flow of combustible material to a furnace or oven when a fire occurs. Such systems involve components such as sensors, relays, solenoids, transformers, and other items which may malfunction. A malfunction could result in the fuel continuing to be delivered even after the fire extinguishing system is tripped. This may defeat the fire extinguishing system.
Thus, there exists a need for a device which will shut off the flow of combustible fuel to an industrial furnace or oven or other type of heating device when a fire extinguishing system is tripped. There further exists a need for a device that is less costly and has greater reliability than prior devices and systems.
In view of the aforementioned deficiencies in previously existing fire-suppressing systems when applied to residential cookstoves, the assignee of the instant invention developed the fire-suppressing systems disclosed in U.S. Pat. Nos. 4,773,485 and 4,834,188. The systems disclosed in these patents have achieved acceptance in the field and have been installed in combination with hundreds of cookstoves. However, there is a need to configure the systems, as basically disclosed in these two patents, in such a way to further facilitate the ease with which householders can readily install the systems. Moreover, configuring the system for relatively easy installation allows skilled installers to proceed more rapidly and less expensively.